Unvented hot water pressure build-up problem

Correct; CITB. Rarely make use of it, though.

That's obvious.

messagenews: snipped-for-privacy@k70g2000cwa.googlegroups.com...

Drivel is not qualified. That is also obvious.

The unvented water heater will work fine, with some remedial work to bring the installation in line with the manufacturer's instructions.

Drivel's suggestions are enticing you up a path of much innovation, expense and uncertainty. Just get it fixed.

He is.

Which may entail ripping the house apart, which is expense and great inconvenience. He can convert the whole thing to a heat bank with work only around the cylinder and problem solved for ever. It may even work out cheaper too.

Er, I'm not really sure. Telford Tornado about 1450mm tall. I suppose it's the 150l model.

Andrew

Doctor Drivel wrote:

messagenews: snipped-for-privacy@k70g2000cwa.googlegroups.com...

There's every chance that the cold feed to the bathroom may well be not too far from the HW cylinder. Putting the cold feed on the same pressure as the cylinder feed should fix all the problems on all the mixers.

IME electrically heated unvented have much higher pressure swings than indirectly heated units. (Because the 24 cycle of electric heating involves bigger temperature swings).

Yep. But getting that with two PRVs can be problematic when one wears at a greater rate than the other.

A shunt pump running when the elements are running usually stops that.

In what? Or did you mean that what you say should be qualified?

An egg and spoon race runners up certificate is not a qualification.

Mat, you are a very confused person.

This has a 12 litre expansion vessel. Fine.

See this:

This is the layout. In your case the pipe from the cylinder to the plate heat exchanger will come from the DHW draw-off. The return from the plate goes into the mains cold feed connection. Between the pump and the cylinder have non-return valve. The mains in goes into the plate before the flow switch. A normal

The pipe from the cylinder to the plate heat exchanger. Have a vent point here and a pressure gauge too. Also have a tee off and compression cap to add inhibitor.

Have a CH filling loop and tee into the cold feed connection and charge the cylinder to 1 bar. Disconnect the loop. There must be no permanent mains connection to the cylinder. The existing unvented controls will do fine.

Set the immersion stats stats, 70 to 80C.

Farnell will supply the flow switch

Flow Switch, makers site: The FS06

This will eliminate any crossflow through the unvented cylinder, as now you heat the mains water instantly. Legionella is vastly reduced. The mains pressure is up to 10 bar or the maximum of the plate heat exchanger, so performance should improve as the DHW is not reduced to 3 to 3.5 bar.

All the work should be local to the cylinder. If you have problems running back pipes to the cylinder to equalise pressure this may work out cheaper and also prevent problems in the future as the hot and cold are at equal pressure. When not at equal pressure a passing basin mixer can force cold into the hot supply.

You don't need an unvented cylinder ticket to do this. It is only when the cylinder is connected to the cold mains supply, or a tank do you need that. A loophole in the law.

The cylinder is working at lower pressures than a normal unvenetd cylinder, so less stress and safer. You may want to insert another pressure relief valve on the pipe from the cylinder to the plate. A normal 3.5 bar CH one will do, and they are cheap. This will blow off first. If it fails then the main 7 bar valve cuts in.

Sounds OK - many thanks. The only problem might be space.

Just one bit I didn't really understand:

compression cap to add inhibitor.

A pressure gauge and a tee I can figure out. But what is a compression cap? Is it just an end (blanking) cap? And what is a vent point? A thing like you get on a radiator that you can vent air from?

Yep. Earey to remove and pour in inhibitor. 22mm.

Yep.

You need not charge it to 1 bar, just enough to fill the cylinder with water.

Please give details of your qualifications. A refusal to do so means you're lying.

Please eff off as you are complete plantpot.

Others will make up their own mind about your reply - or lack of it - to a reasonable question.

Lying about qualifications is a form of fraud.

Please eff off as you are complete plantpot.

Simpler than that, it is fraud and can be punishable by criminal sanctions if done to obtain pecuniary advantage. Sadly, unlike Germany, we don't have a direct criminal law that makes attempting to pass oneself off as an engineer a criminal offence, but we should have.